02/72/05

Draft for discussion

Annals of the ICRPICRP PUBLICATION XX

The Concept and Use of Reference Animals
and Plants for the purposes of Environmental
Protection

EditorJ. VALENTIN

Information contained in this document is preliminary and only forinternal use by ICRP. It should, therefore, not be cited in any
published material until final approval by ICRPPUBLISHED FOR
The International Commission on Radiological Protectionby2[Pergamon logo - including word ‘PERGAMON’]

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CONTENTSPREFACE.................................................................................................................................5
ABSTRACT1.

INTRODUCTION .............................................................................................................7
1.1 Aims
1.2 Background

2. PROTECTING MAN AND THE ENVIRONMENT
2.1 Introduction
2.2 Establishing a common approach
2.3 Building a common science base
3

REFERENCE ANIMALS AND PLANTS
3.1 Introduction
3.2 Criteria for choosing different types of animals and plants
3.3 Achieving an appropriate level of generalization
3.4 A definition of Reference Animals and Plants
3.5 The set of Reference Animals and Plants
3.6 The Reference Deer
3.7 The Reference Rat
3.8 The Reference Duck
3.9 The Reference Frog
3.10 The Reference Trout
3.11 The Reference Flatfish
3.12 The Reference Bee
3.13 The Reference Crab
3.14 The Reference Earthworm
3.15 The Reference Pine Tree
3.16 The Reference Wild Grass
3.17 The Reference Brown Seaweed
3.18 Summary

4 RADIATION DOSIMETRY FOR ANIMALS AND PLANTS
4.1 Introduction
4.2 Current approaches to dosimetry5

THE EFFECTS OF RADIATION ON ANIMALS AND PLANTS
5.1 Introduction
5.2 General data availability on chronic effects of radiation

6 ISSUES RELATING TO THE USE OF DEFINITIONS, TERMS,QUANTITIES AND UNITS
6.1 Introduction
6.2 Recent concepts and terminologies with respect to animals and plants
6.3 Discussion
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7 ASSESSING EFFECTS IN TERMS OF DERIVED CONSIDERATIONLEVELS
7.1 Introduction
7.2 Derived Consideration Levels
7.3 Creating a Reference Set
7.4 Potential applications
9.

SUMMARY AND CONCLUSIONSREFERENCES ...........................................................................................................................

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PREFACEAt its meeting in Vienna in May 2003, the Commission decided to set up a Task
Group, reporting directly to it, to continue the ICRP’s work on issues related to theprotection of the environment. The Task Group was tasked to consider end-points ofinterest for assessing radiation effects in non-human species, to recommend thetypes of reference organisms to be used by the ICRP, and to define an agreed set forassessing and managing radiation exposure in non-human species.
The membership of the Task Group was as follows:
M. E. Clark, USA
N. Gentner, UNSCEAR
L.-E. Holm (Chairman), Sweden
C.-M. Larsson, Sweden
R. J. Pentreath, UK
The following persons served as corresponding members:
R. Alexakhin, Russian Federation
F. Brechignac, France
S. Carroll, The Netherlands
K. Fujimoto, Japan
J. Loy, Australia
G. Pröhl, Germany
C. Robinson, IAEA
A. Shpyth, Canada
P. Strand, IUR
A. Tsela, South Africa
D. S. Woodhead, IUR
Y. Xuan, P.R. of China
The Task Group would like to thank the Swedish Radiation Protection Authority andthe United Nations Scientific Committee on the Effects of Atomic Radiation(UNSCEAR) for making facilities available for Task Group meetings.
The report was adopted for publication by the Commission in ….

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6[PERGAMON logo]

Annals of the ICRP 28:4 (1998) 1-xx

[ICRP logo]

The Concept and Use of Reference Animals
and Plants for the purposes of Environmental
Protection
ICRP Publication xx
Approved by the Commission in xx 2005

ABSTRACT
To be added later

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1.

INTRODUCTION

1.1. Aims(1)

The aims of this report are:-to select, define, and describe in outline a number of Reference
Animals and Plants to be recommended by ICRP;
to consider issues relating to the dosimetric quantities and units that
could be used for such organisms;
to consider the availability of dose models for the selected
Reference Animals and Plants;
to define end-points for assessing radiation effects in non-humanspecies of relevance to environmental management practices;to review the availability of relevant data in order to compile sets of
Derived Consideration Levels for the Reference Animals andPlants; andto further the development of a common approach to the protectionof man and other species.

(2) The report has been produced in order to support the Commission’s latest
comprehensive review with respect to its revised set of recommendations forradiological protection (ICRP, XXXX; 2006).
1.2. Background(3) Environmental protection is now a global issue, and an issue that impacts
upon human activities in many different ways. All forms of actual or potential
threats to the environment are a cause of concern, or of action, or of regulation, andthis includes ionising radiation. The Commission therefore set up a Task Group to
examine these issues in 2000 and, in its report (ICRP, 2003), it considered (a) that a
broader framework for radiation protection of the environment needed to be
developed, and (b) that it should be sufficiently flexible to be applied within thecontext of the many existing and varied approaches to environmental management
generally, and to environmental protection in particular. It also considered that suchan approach should relate as closely as possible to the current system for humanradiological protection, and that these joint objectives could therefore best be met by
the development of a limited number of Reference Animals and Plants.
(4) The Commission accepted these conclusions and, in January 2003, decided
to set up a second Task Group to continue this work by further considering how tomeet expected environmental management needs in relation to environmental
protection. Later that year, in October 2003, the Commission went even further anddecided to establish a new Committee (Committee 5) on the Protection of theEnvironment, to commence work in 2005. The work of the second Task Group wastherefore slightly modified, and given the more general purpose of laying thefoundations for the Commission’s future work in this area, and preparing for thework of the new Committee. In pursuit of these objectives, the Task Group has
78
therefore considered the types of reference animals and plants that could be used by
the ICRP in order to meet future environmental management requirements; the typesof dose models that could be used; the relevance of existing information on radiation
effects for such types of organisms; how such an approach could be used forassessing and managing different levels of radiation exposure in non-human species;
and how such an approach could be harmonised with the Commission’s existing
approach to the protection of human beings.
2.

PROTECTING MAN AND THE ENVIRONMENT

2.1. Introduction(5) The Commission has never made any specific recommendations withregard to the protection of species other than the human being, but in its 1990
Recommendations (ICRP, 1991) it did express the view that:‘The Commission believes that the standards of environmental control
needed to protect man to the degree currently thought desirable will ensurethat other species are not put at risk. Occasionally, individual members of
non-human species might be harmed, but not to the extent of endangeringwhole species or creating imbalance between species. At the present time,
the Commission concerns itself with mankind’s environment only withregard to the transfer of radionuclides through the environment, since thisdirectly affects the radiological protection of man.
(6) The Commission still believes that this judgement is likely to be correct ingeneral terms, because the steps taken to protect the public, by reference to dose
limits for them, have resulted in strict controls and limitations on the quantities ofradionuclides deliberately introduced into the environment. Thus it is probably truethat the human habitat has been afforded a fairly high level of protection through theapplication of the current system of protection. However, there are now otherdemands upon regulators, in particular the need to comply with the requirements oflegislation directly aimed at the protection of wildlife and natural habitats; the needto make environmental impact assessments with respect to the environment
generally; and the need to harmonise approaches to industrial regulation, bearing in
mind that releases of chemicals from other industries are often based upon theirpotential impact upon both humans and wildlife. All of these demands are currently
being met in a multitude of differing ways. This is partly because of the lack ofadvice on the subject at international level, and partly because there are no agreed
assessment procedures, criteria, guidelines or reference data sets with which toapproach these issues in a coherent way. This, in turn, leads to different national
approaches being developed, and makes international harmonisation difficult(7) The Commission therefore recognises that there is a need to explore further
the nature of the ‘risks’ that may apply to other species, how such risks may bequantified, and thus how it can be positively demonstrated that they are, indeed,‘…not put at risk’. The Commission has therefore decided to develop a combined
approach to the protection of humans and other species, and to do so within an
overall framework that recognises the different but complementary aims andobjectives that this involves. The approach recognises that humans, as well as fauna8

9
and flora, are part of the same overall ecosystem; but whereas the protection ofhuman beings has aims and objectives that may be universally applied, the aims andobjectives with respect to the protection of other species will vary considerably,
depending on the species involved, and the nature and the circumstances relating to
the risks to which they are exposed.
(8) The Commission also recognises that the reduction of the frequency ofradiation effects in individual animals or plants does not necessarily imply that theindividual animal or plant is the object of protection. But whereas effects uponecosystems are usually observed at the population or higher levels of organization,
information on dose responses to radiation is usually obtained experimentally at theindividual level. And because radiation effects at the population level - or higher are mediated via effects on individuals of that population, it therefore seems
appropriate to focus on the individual for the purpose of developing an assessment
framework. The Commission also notes that a large number of animals and plants
are already afforded protection at the level of the individual in international or
national law, and it would be inappropriate to provide advice that could not be usedin such legal contexts. The question of whether one should protect individuals or
populations from harmful effects of radiation in any particular circumstance,
however, is not an issue of direct concern to the Commission.
(9) The decision to develop a framework for the assessment of radiation effects
and their consequences in non-human species has not been driven by any particularcurrent concern over environmental radiation hazards. It has been developed both tofill a conceptual gap in radiological protection, and to clarify how the proposed
framework can contribute to the attainment of society’s wider goals ofenvironmental protection. The Commission’s decision to develop an explicit
assessment framework should therefore support, and provide transparency to, suchdecision making processes.
(10) The Commission considers that a framework is needed that can be apractical tool to provide high-level advice and guidance, and thus help regulatorsand operators demonstrate compliance with existing or forthcoming environmental
legislation. It should also be noted that the recommended system is not intended to
set regulatory standards. It does not, however, preclude the derivation of suchstandards after sufficient experience has been gained with the proposed framework;on the contrary, it should provide a basis for such derivation. This framework could
therefore serve as a basis from which national and other bodies could develop, as
necessary, more applied and specific numerical approaches to the assessment andmanagement of risks to non-human species under different circumstances, and thus
with respect to normal situations, accidents and emergencies, and controllable
existing exposures. As was the case with the initial adoption of ICRP’s Reference
Man (ICRP, 1975), further work will be required to develop more fully the concepts
and use of reference animals and plants.

2.2. Establishing a Common Approach(11) The Commission has therefore recognised the need to develop a common
approach to, and scientific basis for, the relationships between exposure and dose,910
and dose and effect, for all living things. In the case of human radiation protection,
this approach has been based on an entity called Reference Man. The Commission
has therefore concluded that a parallel approach would be of value for the protectionof other species, and that this could best be achieved by the development of a small
set of Reference Animal and Plants, plus their relevant databases, for a few types oforganisms that are typical of the major environments. In doing so, the Commission
recognises that this approach cannot reflect the full range of biological diversity, or
provide a general assessment of the effects of radiation on the environment as awhole. However, the Commission considers that this approach could provide thebasis for judgments about the probability and severity of the likely effects ofradiation on such animals and plants, or on other types of organisms that differ in
specific characteristics from the reference types.
(12) It is therefore intended that each reference type would serve as a primarypoint of comparison for assessing risks to animals and plants with similar life cycles
and exposure characteristics. More locally relevant information could be compiled
for any other animal or plant, but each such data set could then be related in some
way to the reference types. Such a combined set of information should then serve asa basis from which national bodies could develop, as necessary, more applied andspecific approaches to the assessment and management of risks to non-humanspecies as national needs and situations arise.
(13) In order to be of practical value, and to assist in their interpretation, theCommission believes that bands of derived consideration levels for Reference
Animals and Plants could be set out in logarithmic bands of dose rates relative tonormal natural background dose rates of the reference organisms. Additions of dose
rate that are below the levels of their background dose rates might then beconsidered to be of low concern, and those that are orders of magnitude greater thanbackground would be of increasingly serious concern because of their known
adverse effects on individual organisms. But the need for any managerial action,
would be dependent upon, for example, factors that would include the numbers andtypes of individuals affected, the nature of the effects, the spatial and temporal
aspects of contamination, and specific legal requirements.
(14) Another prime purpose of the use of a set of Reference Animals and Plants
is to develop a common approach to the protection of man and the environment
under all circumstances. As a starting point, the objectives of such a common
approach might therefore be along the following lines:-

to safeguard human health by preventing the occurrence of deterministic
effects; limiting stochastic effects in individuals and optimising theprotection of populations; andto safeguard the environment by reducing the frequency of effects likely tocause early mortality, or reduced reproductive success, in animals and plants
to a level where they would have a negligible impact on conservation of
species, maintenance of biodiversity, or the health and status of natural
habitats or communities.

(15) The achievement of these objectives should, in turn, be centred on acommon scientific approach, such as the use of sets of reference dose models,reference dose per unit internal and external exposure values, plus reference data
sets of doses and effects for both humans and fauna and flora. Similarly, it is the1011
intention of the ICRP to develop this approach such that there is a commonality inits basic approach to dosimetric modelling, and the interpretation of radiation
effects.
(16) One further advantage of applying the Reference Animals and Plants’approach is that, for any given spatial and temporal distribution of radionuclides,from any source and under any circumstance, one should be able to estimate both therelevant levels of concern with respect to members of the public (based on
Reference Man) and the Derived Consideration Levels, with respect to non-humanspecies (based on Reference Animals and Plants). These two systems will be
independent of each other, but derived in a complementary manner,and based on thesame underlying understanding of the radiation effects on living matter. Also, in apractical sense, they could each be related to the same concentration of a specificradionuclide, within a specific environmental material, at any particular site (Figure
1).
Figure. 1 A common approach for the radiological protection of humans and nonhuman species (Adapted from Pentreath, 2002a, and ICRP, 2003a)
Normal or existing situations, emergency

Environmental radionuclide concentration(s)HUMANSNON-HUMAN SPECIES

Reference Man

Reference Animals and Plants

Dose limits, constraints

Derived Consideration Levels

Decision-making with regard to public health and environment
for the same environmental situation

2.3. Building a common science base(17) Yet another objective of the use of a set of Reference Animals and Plants is
to explore some of the basic concepts of the interaction between radiation and awide range of biological materials, the results of which would be of value not only
in managing the exposures of different species, but might also be of value in11

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generating new insights into the effects of radiation that could be of help in the
management of human exposures. The vast majority of existing data has been
derived for the purposes of human radiation protection, even though much of it has
been derived from studies on other animals. But it is clearly important that theprotection of all species, including man, is based upon the best possible andcomprehensive understanding of the interaction of radiation with living material
generally, and much can be gained by comparative studies. In order to do so,
however, it is essential to develop a common language and basic approach.
(18) Bearing in mind the great variation amongst plants and animals, particularly
with regard to their life cycles (including such features as active and dormant
periods, sexual and asexual reproduction); their life spans (from days to centuries);
and their exposure pathways (where they are in the environment, and what they do),it is clearly also necessary to explore a number of basic issues. These include
considerations of the degree of generality (or not) that can be applied toconsideration of LET, RBE, and radiation weighting factors across the whole of theanimal and plant kingdoms. They also include consideration of the generality of theterminology used, such as chronic and acute dose rates in the context of biota with alife cycle of only days, or for plants that can live for centuries; the relevance (or not)of deterministic and stochastic effects in plants and animals; and, indeed, the extent
to which different biological “end points” and their consequences, such as earlymortality, reduced reproductive success and so on, are of value in different
circumstances.

3.

REFERENCE ANIMALS AND PLANTS

3.1. Introduction(19) The concept of a ‘reference human’ to help manage the many different
situations in which human beings would or could be exposed to ionising radiations
has long been used and recognized by ICRP, which began its work to define the firstreference individual (standard man) in the 1940s and published its firstcomprehensive report on Reference Man in 1975 (ICRP, 1975). The purpose ofReference Man was to create points of reference for the procedure of dose
estimations to humans, for the derivation of relevant quantities and units for theirinterpretation, and for considering the relationships between doses to different partsof the human body and their effects, in the context of human radiological protection.
The Commission has recently adopted a report that provides up-dated information
on Reference Man (ICRP, 2002).
(20) The ICRP has now proposed a similar system of discrete and clearly
defined Reference Animals and Plants for assessing radiation effects in non-humanorganisms (ICRP, 2003a). The approach is based on the concept developed byPentreath (1998, 1999, 2002 a,b, 2003, 2004, 2005). This, first of all, envisaged theuse of a limited number of fully biologically described animals and plants in order todevelop a systematic means of relating exposure to dose, and dose to different
categories of effect that could be interpreted in terms of the normal biology of theseparticular types of animals and plants in environmental situations. The effects
considered to be of relevance were those of early mortality, morbidity, reduced
reproductive success, or some form of observable cytogenetic damage, irrespective12

13of whether or not they arose from stochastic or non-stochastic dose effectrelationships. And secondly that, in order to consider how best to manage different
situations of additional radiation exposure, within the many different contexts of‘environmental protection’, as variously defined in existing environmental
legislation, such information could then be set out so that dose rates known to causesuch categories of effects could be expressed as multiples of the natural backgrounddose rates, for each type of animal or plant, in the form of Derived Consideration
Levels.
(21) This approach therefore acknowledges that one cannot provide a general
assessment of the effects of radiation on the environment as a whole. The
Commission now considers that it should be possible to derive a reasonably
complete set of internally related information for a few types of organisms that weretypical of the major environments. This can best be achieved by drawing upon
existing information, and by selecting organisms that would be amenable to further
study in order to gain a better understanding of their responses to radiation. Thus, byusing sets of dosimetric models and environmental geometries relating to suchreference animals and plants, with clearly defined biological characteristics and life
histories, and applying them to distributions of radionuclides in different
environments, one should be able to make a judgement about the probability andseverity of the likely effects of the radiation exposure on such individuals. One
should then, in turn, be able to make a general assessment of the likely consequences
either for individuals, or for the relevant population (depending on theenvironmental management issue being addressed) using these and otherenvironmental data and information, for such types of animals and plants.
(22) The concept is therefore similar to that used for human radiologicalprotection, in that it is intended to act as a foundation for the making of a number ofbasic calculations, and to serve as a point of reference for drawing comparisons withother – and probably more limited – sets of information on other organisms. Such abasic reference-animals-and-plants approach has been used previously to provide
advice at an international level, primarily in order to establish release rate limits toevaluate potential environmental impacts of radionuclides released into the marine
environment (Pentreath and Woodhead, 1988). This was applied by the IAEA toredefine annual release rate limits for the purposes of the London Convention(IAEA, 1988). It is also similar to the concept of assessment and measurement
endpoints used in ecological risk assessments frameworks (Suter, 1999), and to theapproach recently used in the shape of ‘reference organisms’ (variously describedover a range from multi-phylogenetic assemblages, to generalised phylogenetic
types, down to individual species) to assess ecological radiation exposures in Arctic
and European environmental situations (Brown et al, 2003; Larsson, 2004). The
need for such a basic and generalised framework for environmental protection has
also been strongly supported by the International Union of Radioecology (Strand etal, 2000).

3.2. Criteria for choosing different types of animals and plants(23) There are many factors that have had to be considered in the selection,
description, definition, and potential application of reference animals and plants, andthe Task Group was greatly assisted in their consideration of these issues by being
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able to draw upon the many studies, seminars, conferences, and research
programmes that have recently been held on this general topic, including thefollowing: symposia on the protection of the environment from ionising radiation in
Stockholm, (Amiro et al, 1996), Canada (Anon, 2001), Darwin (IAEA,2003), andStockholm (IAEA, 2005); two IAEA Reports (IAEA, 1999, 2002); the IUR (Strand
and Oughton, 2002); the NEA (2002); and the results of the EPIC and FASSET
projects (Brown et al, 2003; Williams, 2004).
(24) It is also evident that limits have to be placed on the level of complexity ofthe system that could or needs to be developed by the ICRP, both with regard to thedose models that are required and the level of interpretation that needs to be appliedwith respect to different categories of radiation effect. Limits have also had to beplaced on the number of reference animals and plants that could be used in such asystem.
(25) Given that the objective is to provide a starting point for the assessment of
exposure, radiation dose, and possible dose responses for such an enormous varietyof living animals and plants, it is clearly not easy to select a few types for the
purposes of creating a small reference set. A number of basic scientific criteria canand have been considered, but perhaps the first to note is that of what the
information is likely to be used for, and under what circumstances. These were
anticipated to include the following:- requirements to meet new or expected environmental legislation, particularly in
relation to wildlife conservation and habitat protection, that may apply toindividual animals and plants, their populations, or to specific habitats andcommunities, and that may need to be applied to existing practices;- requirements for ‘environmental impact assessments’ in relation to existing or
proposed practices that, as well as including the above requirements, may
necessitate evaluations to be made with respect to potential impacts on otherforms of environmental management, such as those relating to fisheries,
agriculture, and so on, and of the consequences of major accidents andemergencies; and- requirements to achieve consistency in regulatory approaches to large
industries, particularly with regard to the need to consider, explicitly, not only
their potential impact on the general public but also their potential impact on
the environment generally.
(26) The feature common to all of these requirements is the need to have aconsistent and transparent approach to relating exposure to dose, and then relatingdose to what is known about different sorts of effects on different types of animals
and plants. But it is appreciated that the application of this type of information willvary substantially at national or regional level.
(27) Bearing these points in mind, the Commission considered that a mixture ofanimals and plants was needed that reflected both the variety of operational andregulatory requirements, and the need to be pragmatic in terms of developing aflexible framework to accommodate future needs and the acquirement of new
knowledge. It would therefore appear that, in relation to the anticipatedrequirements:
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for the purposes of new or expected environmental legislation, particularly
with regard to wildlife and habitat conservation, any likely list of candidate
types would need to include a number of vertebrate animals, such as a bird
and a mammal, and possibly even a reptile or amphibian, and that wetland
habitats appeared to be particularly subject to international and national
concerns, often with respect to the transboundary movements of wildlife
within geographic regions;-that for evaluations in relation to environmental impact assessments,
particularly where these interface with other forms of environmental
management, any list would necessarily require examples of animals andplants that were relevant to such practices as fisheries, agriculture, andforestry; and-with regard to achieving consistency in regulatory approaches, it was notedthat in other forms of pollution control a number of ‘toxicity-test’ typeorganisms are already routinely used, and thus some overlap with such typesof organisms would be desirable, and that because ecotoxicological studies
are also often used in pollution control, it would be important to ensure thatthe total reference set had a reasonable coverage of the major ecologicalcompartments of terrestrial and aquatic ecosystems.

(28) Notwithstanding such requirements, however, it is also necessary to be
pragmatic. It is simply not possible to gain the necessary information about radiation
effects on some types of wildlife that are the subject of conservation measures, orare fished or otherwise harvested commercially in aquatic and terrestrial
environments. Nor is it possible to gain sufficient information to represent the wide
range of potential exposure situations of animals and plants in the environment
under planned, existing, or accident and emergency situations. Fortunately, however,quite a lot of information does already exist that is relevant to the above
requirements. Various animals that have commercial value, and several agricultural
crops and other plants have been studied in some detail. These, in turn, occupy arange of ecological niches, and display a range of different life histories.
(29) Collectively, therefore, in selecting a small but practical set of reference
animals and plants, the following criteria were used:--that there is a reasonable amount of radiobiological information alreadyavailable on them, including data on probable radiation effects;
that they are amenable to future research, in order to obtain the necessary
missing or imprecise data, particularly with regard to radiation effects;
that they are considered to be typical representative fauna or flora ofparticular ecosystems;
that they are likely to be exposed to radiation from a range of radionuclides
in a given situation, both as a result of bioaccumulation and the nature of
their surroundings, and because of their overall lifespan, lifecycle andgeneral biology;
that their life-cycles are likely to be of some relevance for evaluating total
dose or dose-rate, and of producing different types of dose-effect responses;
that their exposure to radiation can be modelled using relatively simple
geometries;
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that there is a reasonable chance of being able to identify any effects at thelevel of the individual organism that could be related to radiation exposure;and that they have some form of public or political resonance, so that bothdecision makers and the general public at large are likely to know what theseorganisms actually are, in common language.

(30) A final consideration is that of how best to describe the chosen selectedreference animals and plants, bearing in mind that it has not been the intention to
select particular species, but equally not to generalize to the extent that thecharacteristics of the selected types are of little biological meaning.

3.3. Achieving an appropriate level of generalization(31) The taxonomic framework for past and present life on Earth has always
been somewhat flexible, and is still the subject of much debate. Nevertheless,virtually all forms of life can be, simply for convenience, divided into either the
animal or plant kingdoms, with viruses and similar micro-organisms being grouped
separately. Bacteria, too, are often considered as a separate ‘kingdom’, although they
have also been – and sometimes still are – grouped with the plants. The same applies
to the fungi. Single-celled organisms have also been considered separately – as theProtista.
(32) The classification of animals and plants is primarily a reflection of theirmorphological characteristics, plus physiological and biochemical features, andoften draws upon what is known or assumed about their evolutionary history. Suchapproaches are now greatly strengthened by the use of DNA analyses. Animals aregrouped into Phyla, on the basis that each Phylum has, more or less, the same ‘bodyplan’ (such as chordates, or echinoderms, or arthropods) and within each Phylum
they are further grouped into Classes, then Orders, then Families (which share‘typical’ traits and features), and then Genera as the number of features they have incommon increases; finally, Genera are divided into species. There is no absolutedefinition as to what a species actually is, but it is usually taken as a description ofindividuals that (it is either known or expected) can only produce fertile offspring asa result of mating with similar individuals. In some cases, even further distinctions
are made – into sub-species, or into races and varieties. Plants, too, are characterized
in relation to features such as anatomy, embryo characteristics, and biochemistry,
and are similarly classified except that they are usually grouped into Divisions rather
than Phyla. Features that differentiate either animals or plants at the level of Class orOrder are often fairly detailed, and may be more a reflection of their evolutionary
history than a factor that is relevant to their general biology today. Such groupings
are subject to considerable fluctuations and are the subject of academic study anddebate. Thus there are no internationally accepted ‘rules’ on classification above
Family (or ‘Super Family’) level, and this level of generalisation has therefore beensuggested as being the most suitable (Pentreath, 2002 b, 2005; Pentreath andWoodhead, 2001).
(33) The total number of living species of animals and plants is not known withany certainty, although the majority of ‘large’ organisms have probably been thesubject of description and classification. Thus probably 99% of birds and 90% ofother land vertebrates have already been described (Goto, 1982). It is generally
assumed that there are certainly well over a million species of animals, and at least16

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half that number of plants on Earth at present; although some recent estimates place
the former as high as 3 to 4.5 million, and the latter as low as 0.35 million(Sauchanka, 1997). New species of animals and plants have been described in recent
decades at the rate of about 10,000 per year, and approximately half of these are
insects, the remainder consisting largely of a wide variety of other invertebrate
animals (particularly from the marine environment), and plants.
(34) Animals usually have between 12 and 60 pairs (2n) of chromosomes, butthere is considerable variation, even within Orders and Families (for example, in the
Diptera (flies) 2n varies from 4 to 20; in the Lepidoptera (butterflies and moths) it
varies from 14 to 446). The molecular biology of plants is much more variable thanthat of animals, with more frequent recombination and re-assortment of genes duringmeiosis. Nuclei, mitochondria, and plastids within plant cells, all have their distinct
DNA systems. Polyploidy is common in plants (50% of all flowering plants),
usually because a diploid (2n) plant, by irregular division, gives rise to a tetraploid(4n) plant. Then, as a result of pollination, triploid (3n) plants are formed. These areunable to produce gametes compatible with either ‘parent’, and thus the 2n and 4n
forms often diverge because of the resultant genetic isolation (Collinson, 1988).

3.4. A definition of Reference Animals and Plants(35) Because no clear algorithm for the selection of Reference Animals andPlants can be defined, their selection has to be made on best judgement, bearing in
mind the need to keep the total number low, to try and cover terrestrial, freshwaterand marine environments, and to satisfy the various criteria discussed above.
(36) Based on all of these criteria, therefore, and in an attempt to be consistent
with the concept of Reference Man, a Reference Animal or Plant can be described asfollows. A Reference Animal or Plant is a hypothetical entity, with the assumed
basic biological characteristics of a particular type of animal or plant, as describedto the generality of the taxonomic level of Family, with defined anatomical,
physiological, and life-history properties, that can be used for the purposes ofrelating exposure to radiation dose, and relating dose to different categories ofeffect, for that type of living organism.
3.5. The set of Reference Animals and Plants(37) Working within this definition, and taking into consideration both the needs
and the selection criteria, an initial ‘set’ of reference animals and plants has been
identified, as set out in Table 1. A deliberate emphasis has been placed on vertebrate
animals but, in compiling the overall ‘set’, consideration has also been given to therange of habitats covered (Table 2), the variety of life histories and life spans
represented, and the potential for extrapolating the basic ‘Reference’ animal or plantdata to other forms of animal or plant, or to place them in other environments. Thus,
again bearing in mind that the primary purpose is to use the reference animals andplants to relate exposure to dose, and dose to effect, it should be possible to adapt
the basic data in relation to, for example, the marine flatfish to that of a similar fishin an estuarine situation, or to adapt the freshwater salmonid fish (trout) data to
those of a marine ‘round’ fish, and so on. Equally, however, a balance has had to be
struck between keeping the descriptions and numerical information as simple as17

18
possible, proportionate to the amount of radiobiological information currently
available, and the purposes to which the data will be put.

Table 1. Subjective assessment of the types of Reference Animals and Plants
against some key criteria used in their selection (+low; ++medium; +++highaffinity).

Deer
Rat
Duck
Frog
Trout
Flat fish
Bee
CrabEarthworm
Pine tree
Grass
SeaweedLegislation Use in Humanrelating to toxicity resource
wildlife
testing
protection
+
++
+
+++
+++
+
++
+
++
+++
+++
+
+++
+
+
++
+
+++
+++
+
+++
+
+++
+

Data on
Data on Amenable Public
radionuclide radiation to further resonanceaccumulation effects
study
+
++
+
+
+
+++
++
+++
++
++
++
+++

+
+++
+
+
+++
++
+
+
+
+++
+++
+

+
+++
+++
++
+++
++
+++
++
+++
+++
+++
++

+++
+
+++
++
+++
+
++
++
++
+++
++
++

(38) The set is essentially one of ‘wild’ animals and plants rather thandomesticated ones. With regard to farm animals, primarily large mammals that live
essentially in a human environment, it was considered that the use of the humananimal itself was probably sufficient for such managed environmental or ecologicalsituation. The inclusion of the deer in the list was however considered to provide
some link, because such animals are farmed in some countries.
Table 2. General types of selected reference animals and plants in relation to theirecological spread.
Organism

Terrestrial

Freshwater[Reference Man]

[X]

Deer

X

Rat

X

Duck

X

X

Frog

X

X

Trout

X

Flat FishBeeMarine

X
X

X

Crab

X

18

X

19
Earthworm

X

Pine Tree

X

Grass

X

X

Brown SeaweedX(39) The following descriptions are intended simply as brief introductions to thetwelve types of Reference Animals and Plants that have been selected.
3.5.1. The Reference Deer(40) Large herbivorous mammals occur over most of the temperate regions of
the world, and extend into the arctic and tropical regions. Of these, some of the mostubiquitous are members of the deer Family (Cervidae). Deer occur throughout
Europe, Asia, Africa, and the Americas, and various native species have been
introduced into other countries, including throughout the southern hemisphere, forvarious reasons. Deer are therefore well studied and have been raised in various
forms of captivity. The reference deer is taken to be a medium sized woodland deer.
3.5.2. The Reference Rat(41) There is probably more information on the effects of radiation on rodents
than on any other mammal, with the exception of the human being. Rats and mice
(Muridae) have been used extensively in laboratory experiments for a vast range ofstudies, particularly in relation to human medicine, including a large number in
relation to the metabolism of radionuclides, and on the effects of radiation from bothinternal and external sources. In the environment they are fairly ubiquitous, with aworldwide distribution. Although generally regarded as a human pest, some species
are rare, threatened, and thus legally protected in some countries. The reference rat
is assumed to be nocturnal, feeding at night and resting during the day in a burrow.
3.5.3. The Reference Duck(42) Ducks (Anatidae) occur in rural and urban areas, and a number of species
have been domesticated in various parts of the world and hence bred in captivity andused as a human food source. Wild ducks are also taken for food in some countries,
but many species are increasingly protected, and ‘wildfowl’ generally are regarded
as vital components of wetland ecosystems; and wetlands are, in turn, variously
protected to provide habitats for wildfowl, either in relation to breeding or in relation
to feeding and resting areas for migratory species. Ducks, in general, can thus beviewed as birds that are ‘typical’ of wetland areas, and their exposure to radiation
throughout their life histories could arise, externally, from radionuclides on soil or in
fresh, estuarine, or sea water, and internally from the ingestion of a wide range ofaquatic animals, and from both aquatic and terrestrial plant materials. The reference
duck is assumed to have the characteristics of a typical ‘dabbling’ duck. (These are
the most ubiquitous, being found in urban and rural areas.)
3.5.4. The Reference Frog
(43) Frogs and toads are also typical of wetland areas in many parts of theworld. Some species are extremely rare and many are now protected. Wild frogs andtoads are taken for human food in a number of countries, and some species are19

20
farmed as a food source. They have been used extensively as teaching aids. With atypical life cycle involving an aquatic egg, a tadpole stage, and then a terrestrial
adult, frogs are likely to encounter a wide range of potential exposure situations inboth freshwater and terrestrial environments. The reference frog is taken to be amember of the Family Ranidae, living in a temperate region around fresh water,
spending its non-breeding time out of water, and hibernating over the winter period
in mud.
3.5.5. The Reference Trout(44) Salmon and trout (Salmonidae) are regarded as biological indicators ofgood water quality and are the subject of much environmental and fisheries
legislation. They have also been the subject of many laboratory studies on fish
physiology, and on radionuclide metabolism and radiation effects, as well as being
used to investigate the accumulation and effects of many other environmental
contaminants. They are used in toxicity tests for a range of pollutants. Trout, inparticular, are also widely farmed throughout the world, and salmon are now farmed
in many countries. Salmonid fish live in both marine and fresh waters. They lay theireggs on the bottom of streams and the adults live in the water column. The reference
salmonid is taken to be a ‘trout’ rather than a ‘salmon’ in order to avoid thecomplication of migratory effects of the salmon from fresh water to the marine
environment. It is therefore assumed to live its life in the same body of water,
spawning in a stream that runs into that water.
3.5.6. The Reference Flatfish(45) Teleost (bony) flatfish species are the basis of commercial inshore fisheries
in many parts of the world, and a number of species are farmed commercially. They
have been the subject of many laboratory studies, and extensively studied withregard to their accumulation of radionuclides and the effects of radiation. In contrast
to salmonid fish, teleost flatfish produce eggs that float in the water column. The
larvae remain in the water column for several weeks and thus, together with theeggs, form part of the plankton. The larvae metamorphose and settle on the sea bed,
both juveniles and adults living predominantly in or on the bottom sediments. They
inhabit both marine and brackish waters. The reference flatfish is taken to be amember of the Pleuronectid Family, although whether or not it is ‘right-eyed’ is ofno particular relevance. It is a shallow-water, bottom feeding fish
3.5.7. The Reference Bee(46) There are probably more species of insects on the planet than of all otherforms of life put together. They play a vital role in the ecology of terrestrial
ecosystems, as predators and prey, parasites and scavengers, and as pollinators offlowering plants. A few species are directly harmful to man, by way of carrying
diseases, although immense indirect damage can also be done to crops and building
structures by other species. Equally, however, many species are essential for croppollination, and hence in human food production. Many species are also legally
protected, either because of their own ‘value’ (such as butterflies) or because they
provide a vital role in maintaining the ecology of other ‘valued’ animal or plant
species. The most studied, and easily reared, insects are the bees. Although the
majority of bees are solitary and relatively short lived, the best studied are the social
bees, particularly the honeybees. The reference bee is therefore assumed to be atypical social (Family Apidea) bee.
20

21
3.5.8. The Reference Crab(47) Crabs, and lobsters, are amongst the few types of invertebrate animals thatgrow to a sufficiently large size (up to 20kg in weight and with ‘leg spans’ of over3m) to warrant the need for more complex geometries to estimate dose rates frominternal and external sources. They also have comparatively long life spans. Crablarvae form part of the plankton, and their size and feeding patterns are very similar
to other types of crustaceans that spend their entire life cycle as part of the plankton.
Although the majority of crabs are marine species, there are many that inhabit
brackish waters, and fresh waters, and some are essentially terrestrial. Crabs arewidely taken for human food in coastal waters all over the world, and many species
are farmed commercially. Their biology has therefore been well studied, and they
have been the subject of many radiobiological studies and radiochemical analyses.
The reference crab is taken to be a temperate water crab with a reasonably large
adult size; it is essentially a crab of the Cancrid Super-Family.
3.5.9. The Reference Earthworm(48) Earthworms make a large contribution to the total weight or biomass of
soils, particularly in temperate regions. They play a vital part in the breakdown ofdead plant and animal material in soil and forest litter, and thus in soil fertility, as
well as in the maintenance of soil structure and aeration. They also provide a foodsource for a large variety of mammals and birds. They have been extensively used in
the toxicity testing of inorganic and organic chemicals, particularly insecticides,
fungicides, herbicides, and heavy metals. Some species grow and reproduce well inorganic wastes and have been used to feed both fish and livestock. They have also
been used in the amelioration of contaminated land, in land reclamation (such asmine wastes), and as indicators of environmental contamination. The reference
earthworm is taken to be a member of the Lumbricid Family, living in the temperate
zone.
3.5.10. The Reference Pine Tree
Pine trees (Pinaceae) occur naturally across the whole of the Northern hemisphere,
from the Arctic Circle to just south of the Equator, in a wide variety ofenvironments. They have also now been introduced into many southern hemispherecountries worldwide. They have been extensively used by man for building
materials, for fuel, and for resin. They have also been well studied with regard totheir physiology and general biology, and are easily cultivated. There is also a large
amount of information on them with regard to exposure to radiation and its effects.
3.5.11. The Reference Wild Grass(49) Grasses (Graminaea) of one form or another are the predominant plants
throughout much of the terrestrial environment. They occur naturally in a wide
variety of forms, including reeds and bamboos, as well as the more familiar cereal
crops and the dominant plants of natural pasture land. They serve as food for a wide
range of herbivorous mammals, including (as herbage) domesticated forms of cattle,
sheep, and horses. They are also the basic food crop for humans all over the world.
Their biology has therefore been well studied, including their accumulation of awide range of chemicals. The ‘Reference Wild Grass’ is taken to be a ‘barley type’
grass.
21

22
3.5.12. The Reference Brown Seaweed(50) Seaweeds are the principal macroscopic plants of the marine environment,
occurring in coastal waters all over the world. Some species are commerciallyharvested for human food, for fertilizer or for use as cattle food, and some are
harvested for the extraction of alginates and gums. Seaweeds have also been used
extensively to examine the adsorption, or absorption, of a wide range of chemicals,particularly metals, in marine or brackish water environments. Their chemicalcompositions have therefore been well studied, and they have also been used
extensively as indicators of the dispersion of radionuclides in the aquatic
environments. And, because some species are eaten by humans, these have been
extensively monitored in the vicinities of coastal nuclear sites. The reference brownseaweed is taken to be a Cyclosporean brown intertidal seaweed, living in such a
position that it is covered by seawater for 75% of the time. It has a simple life cycle,
in that the adult plant is a diploid sporophyte that has male and female conceptacles
on the same thalli (monoecious).
3.5.13. Dimensions of Reference Animals and Plants(51) Possible dimensions of Reference Animals and Plants are shown in Table 3,
as represented by solid ellipsoids for primary phantom dose modelling.
Table 3: Possible dimensions of Reference Animals and Plants.
Organism

Major axis ofellipsoid (cm)Minor axis ofellipsoid (cm)

Adult Deer

130

60

60

Rat pup

2

0.6

0.5

Rat

20

6

5

Duck egg

6

4

4

Duck

30

10

8

Frog egg1

1

1

Tadpole

1.5

0.75

0.75

Frog

8

3

2.5

Trout egg

0.25

0.25

0.25

Trout

50

8

6

Flatfish egg

0.02

0.02

0.02

Flatfish

40

25

2.5

Bee larva

1.5

0.75

0.75

Bee

2

0.75

0.75

Bee colony (natural)

60

30

30

Crab egg

0.03

0.03

0.03

Crab larva

0.03

0.03

0.03

Crab

20

12

6

Earthworm egg

0.5

0.5

0.5

Earthworm (elongated)

10

1

1

Pine tree trunk

3500

150

150

Grass spike

5

1

1

Brown Seaweed

50

0-5

0.5

22

Second minor axisof ellipsoid (cm)

23

3.6. Summary(52) These twelve animal and plant types - as adults, eggs, or larvae, as
appropriate – therefore occupy a range of environmental situations and thus potential
exposure to radionuclides from different sources. They range considerably in size
but, as a basic step, each could be simplified into simple shapes for the basis of
making primary phantoms for the purposes of estimating doses received under
different circumstances. The range of sizes that might be expected is indicated inTable 3, and aspects of dosimetry are discussed in the next section.
4.

RADIATION DOSIMETRY FOR ANIMALS AND PLANTS

4.1. Introduction(53) Although many different approaches have been used to estimate the doses
received by animals and plants, from both internal and external sources, they have
many features in common. A number of international panels and meetings haveaddressed various aspects of dosimetry, particularly with respect to aquaticorganisms (IAEA, 1976, 1979, 1988; NCRP, 1991). All of the approaches used have
had to strike a balance between the complexity of the modelling that is theoreticallypossible, and the practical availability of relevant data to apply to them. There are
two issues here: one is the vast range of shapes and sizes that occur throughout the
animal and plant kingdoms; the second is the fact that radionuclide concentrations inanimals and plants display all of the variations amongst tissues and organs that occur
in human beings, but there are few internally consistent data sets for any one
particular type of animal or plant. Thus an extreme simplification has often been
made, and that is the reduction of the whole organism to a simple shape.
(54) Empirical expressions, involving energy-dependent parameters, have beendeveloped to describe absorbed dose distributions about point sources of α, β, and γ
rays (Loevinger et al, 1956; Berger, 1968; 1971; Harley and Pasternack, 1972).
These expressions have then been integrated over defined source distributions togive estimates of the dose rates at specified points within the targets, from which
average dose rates can be calculated (Brownell et al, 1968; Ellett and Humes, 1971).
The targets used have been described as solid spheres or cylinders (IAEA, 1976) or
solid ellipsoids (Pentreath and Woodhead, 1988; IAEA, 1988; NCRP, 1991), andestimates made of dose rates from external and internal sources. Much more detailed
models were developed by Woodhead (1970, 1979) to describe the special cases of
exposures of the embryos of developing fish eggs.
(55) For the marine environment, several generalised faunal types (fish,
crustaceans, and molluscs) have already been used to produce a set of dose rate perunit concentration values for 104 radionuclides, and these have been normalised tounit ambient water concentrations to estimate dose rates from both external and23

24internal sources by applying tabulated values of concentration factors and kd values(IAEA, 1985(NB now updated)) to the calculated dose coefficients (Pentreath andWoodhead, 1988). These values (dose rate per unit water concentration values)
were applied by the IAEA (1988) to oceanographic models of radionuclide
dispersion in order to assess the environmental impact of the deep-sea disposal of
low-level radioactive wastes.
(56) More recently, Amiro (1997) has produced sets of ‘radiological doseconversion factors’ for screening potential ecological impacts with respect toradionuclides in soil, water, and air. And generalised dose models, for a similar
purpose, have been produced by the USDOE (2002).
4.2. Current approaches to dosimetry(57) With regard to the use of a solid ellipsoid, the majority of studies haveestimated the proportion of radiation absorbed within the volume of the ellipsoid byusing formulae that describe the distribution of radiation doses around point sources
within it, and then integrating the resulting doses over all hypothetical point sources
and point receptors. This can be done analytically for simple cases, but for more
complex cases, and for greater convenience, it is preferable to use numerical models.
Such models can now be run relatively easily. The approach developed by
Copplestone et al (2001) is particularly useful; it uses polynomial functions that arederived from the point-isotropic specific absorbed fractions (the fraction of energy
absorbed per gram of absorbing medium at a distance r cm from a point source of γ
ray photons of energy E MeV). Such data for protons were calculated and publishedby Berger (1968) to provide a continuous interpolation for each discrete photon
energy. Pairs of co-ordinates, both of which lie within the specified ellipsoid, areselected using a random number generator, the distances between them calculated,
and these steps iterated a few thousand times, averaging throughout the mass of theellipsoid, in order to obtain estimates of (FE), the fraction of energy emitted within
the volume that is also absorbed within it.
(58) Tabulated dose distributions around point sources for β particles have also
been produced by Berger (1971), but although the same computational method could
be used as for γ ray photons, the process is computationally inefficient because of
the decay schemes and range of energies of β particles in such radionuclides.
Copplestone et al (2001) therefore derived a method that estimates β-particle
absorbed fractions by selecting three co-ordinates at random within the defined
ellipsoid, generating a vector through them defined by randomly selected angles,
calculating a distance along the vector to the surface of the ellipsoid and thus, again
within a few thousand iterations, deriving point estimates of FE.
(59) With regard to α particles, because their range in living tissue is small, it isassumed that the absorbed fraction is unity for the sizes of organisms considered;relatively simple equations can therefore be used to estimate dose distributions forinternally incorporated radionuclides (eg Harley & Pasternack, 1972). Doses fromexternal α particles are generally taken to be zero, but it should be noted that, forsmaller entities (such as benthic eggs or larvae) this aspect needs to be addressed
explicitly (Woodhead, 1979)(60) Copplestone et al (2001) used this numeric approach to calculate a set of‘dose (rate) per unit concentration factors’, where the unit concentration factors
24

25
refer either to the concentration of the radionuclide externally in different media(uniformly distributed) or internally. A set of values for 9 radionuclides was derived,for a number of ‘reference organism’ solid ellipsoid geometries. And essentially thesame method has since been used by Vives i Batlle et al (2004) for an even greater
range of aquatic biota, and for 43 radionuclides, both natural and artificial, including
various sets of daughter nuclides.
(61) Recent advances have also been made with regard to dosimetry using
Monte Carlo methods. These have been used to estimate dose rates for 25
radionuclides (individually, for radionuclides with half lives > 1 day) in a range ofNorthern latitude animals and plants, expressed as ‘dose conversion factors’ as partof the EPIC programme (Brown et al, 2003). Similarly, as part of the FASSET
programme, sets of ‘dose-rate conversion coefficients’ for β and γ emitters havebeen calculated for 37 radionuclides for cylinder and ellipsoid ‘phantoms’ over arange of 0.2 g to 550 kg, taken to represent a range of generalised terrestrial animaland plant types (Taranenko et al, 2004). In both cases, the dose rate conversion
coefficients for external sources of photon exposure have been expressed either as
dose-rate per unit concentration of a radionuclide uniformly distributed in the upper
10 cm or 50 cm of soil, or per unit area of a radionuclide in the region of the soil
surface. The air kerma at different heights above the ground for various phantoms
were also calculated using Monte Carlo simulations.
(62) Thus various methods are now available to estimate dose rates to a wide
range of animal and plant types, in a wide variety of environmental geometries, forall radionuclides at the ‘whole-body’ level. Current limitations are to the applicationof this approach due to the lack of available data, rather than in the models
themselves. Nevertheless, all of these ‘whole-body’ approaches necessarily makesimplifications with regard to the distribution of radionuclides; these are usuallyassumed to be evenly distributed, both internally within the organism, andexternally. Again, this is as much a reflection on the lack of available data as it is of
dosimetric expertise, and yet the distribution of some radionuclide radionuclides thatare known to be significant contributors to the total dose rates are known to varyconsiderably in concentration from one organ to another. Some information isavailable, and the influence of differential radionuclide distributions within
ellipsoids has been examined in a general way by Pentreath and Woodhead (1988)
using examples of one order of magnitude internal discrimination, or preferential
accumulation, relative to the whole body accumulation for β emitting radionuclides.
But if clear relationships between dose rates and specific biological effects are to bebetter understood, then it is clearly necessary to have more precise information about
the dose rates received by the relevant organs or tissues. And although mostdosimetric models have been developed for ‘adults’, other stages in the life cycle(which not only have different geometries but may exist in an entirely different partof the environment) also need to be studied in more detail.
(63) There is clearly a need for greater consistency and clarity in the use of theterms used to relate exposure to dose in these various exercises. The allowance fordifferences in relation to radiation quality is also an important factor in this
discussion. This, however, also depends upon what is known about radiation effects
for different plants and animals, as discussed in the next section.
(64) Finally, one also has to consider the data bases relevant to estimating theinternal exposure of animals and plants relative to the concentrations in the ambient25

26
environment. Such data often take the form of so-called concentration factors foraquatic organisms, and as transfer factors for terrestrial biota. There are manysummaries and tabulations of such data, including those relevant to the selected listof Reference Animals and Plants. In the majority of cases, however, the data havebeen derived with respect to estimating the dose to humans following consumptionof the relevant biota, and therefore often only refer to the ‘edible parts’, which are
not necessarily those of greatest interest in terms of the relationships between doseand effect for the organisms themselves. Nevertheless, such data bases can be
examined more closely, and are probably sufficient to enable initial estimations ofdose per unit environmental concentration for a large number of radionuclides to be
made.
5.

THE EFFECTS OF RADIATION ON ANIMALS AND PLANTS

5.1. Introduction(65) At the sub-cellular level, there is now a considerable body of knowledge
relating to the mechanisms by which radiation damage is caused (ICRP, 2003c).
This has been achieved primarily by way of examining the fine structure of energy
deposition from radiation tracks in the DNA molecule, largely as a result of thefurther development of Monte-Carlo track structure codes. It is therefore now
generally recognised that double and single strand breaks in the DNA sugarphosphate backbone, plus a variety of damaged DNA bases, can combine together inclusters so that a substantial fraction of the total damage is closely spaced. These
effects arise from a combination of events induced by the main tracks and secondary
electrons, plus secondary reactive radical species. There is also evidence that boththe frequency and complexity of clustered damage depends upon the linear energy
transfer (LET) of the radiation. In this respect it is also interesting to note that suchdamage, being complex and clustered, is somewhat different from the damage that
may arise from oxidative attack by reactive chemical radicals, which is usuallyrandomly distributed and relatively simple.
(66) Furthermore, it would also appear that it is the error-prone repair ofchemically complex DNA double strand lesions that best explain cellularradiobiological responses such as the induction of chromosome aberrations, genemutation, and cell killing. And DNA damage-response and repair processes are now
also considered to be major determinants of dose, dose rate, and radiation quality
effects in cells. Most of this information has been channelled into an understandingof the effects of radiation on humans, particularly with regard to the induction ofstochastic effects in different organs and tissues.
(67) This basic understanding of the effects of radiation at a sub-cellular level isextremely important, but it also needs to be linked to the effects that are observed intissues, organs, and of course the whole organism. There is a large data base on theeffects of radiation on plants and animals and all of it, or limited sections of it, havebeen regularly reviewed from one standpoint or another over the last decade or so(IAEA, 1992; UNSCEAR, 1996; Whicker and Hinton, 1996; Pentreath, 1996;
Copplestone et al, 2001; Real, et al, 2004). The data reviewed have been derived indifferent ways and for different purposes. Some studies have examined the relative
effects of high dose rates on different types of animals and plants, presumably in thecontext of evaluating the impact of nuclear weapons. Many studies have been26

27
carried out on mammals in order to provide information of relevance to humanradiological protection. And some studies have been carried out to study the effectsof radiation on specific biological end points, such as mutation rates in insects.
(68) Experiments have therefore been carried out at high dose rates over shortperiods of time, and at lower dose rates over extended periods of time. Someexperiments have been carried out by irradiating animals and plants under external‘field’ conditions; others have been carried out under carefully controlled indoor
laboratory conditions. Some have involved small groups of individuals; others havesimultaneously exposed breeding ‘populations’. Some studies have used carefully
calibrated external sources of radiation; others have involved the use of external orinternal exposure to radionuclides in the laboratory, where the actual doses received
are not always well described. Some have attempted to relate selected biologicaleffects to ambient radionuclide concentrations, or ambient dose rates, inenvironmental locations that have been contaminated in various ways, although such
‘epidemiological’ type studies are few. Thus the range of individual species studied
has varied enormously, as have the modes of exposure, the dose rates, and theselection of biological effects recorded. It is therefore not surprising that the
majority of reviews conclude with broad estimates of dose-effect relationships, andthat such ranges demonstrate considerable uncertainty and overlap.
5.2. General data availability on chronic effects of radiation(69) With an increasing awareness of the need to develop a more systematic
approach to this subject, several recent reviews have examined the available database of radiation effects with respect to different biological end points across various
animal and plant groups. A number of different approaches can and have been used
to organize the data. Particularly valuable has been the FASSET Radiation Effects
Database (FRED), developed as part of that project (Larsson, 2004; Real et al,2004). This consists of about 25000 entries, arranged according to four ‘effects’categories across 16 wildlife groups, with an additional differentiation between acuteand chronic exposures.
(70) Experimental data are usually reported with experimental dose rates
averaged over periods of hours, days, or years. Summaries of the data are therefore
often arbitrarily organised into such bands of dose rates. With regard to mammals,
effects pertaining to early mortality, mutation, and reduced reproductive successhave been recorded for different species within dose rates ranging from 0.1 to 1
mGy h-1 (Real et al, 2004). For other vertebrates, the data base is poor with regard tobirds, reptiles, and amphibians, but there is a substantial amount of information
relating to both freshwater and marine species of fish, primarily relating to
reproductive success but also with respect to humoral immune responses indeveloping embryos. These types of effects, for which the information is by nomeans consistent, have been reported at dose rates estimated as low as 8.3 to 83 μGyh-1, but similar effects have not been detected at 9 mGy h-1. Various effects on adults
relating to reproductive success have been reported in the range of 0.1 to 1 mGy h-1,
but with little consistency at dose rates of less than 0.2 mGy h-1. At higher dose
rates, a wide range of effects have been seen and categorised in all vertebrates, and itis therefore difficult to draw conclusions about any real differences inradiosensitivity between mammals and other vertebrates (Real et al, 2004).

2728(71) A large data base exists on the radiation sensitivity of terrestrial plants, in
relation to both chronic and acute exposures, and these arise predominantly fromstudies in Russia. The data base has again been reviewed recently by Real et al(2004). The data have been derived both from controlled experiments and from theaccidents in the Eastern Urals and at Chernobyl. Many of the data relate tomorbidity, with detrimental effects in pine tree species occurring at dose rates of theorder of 2.4 mGy day-1, and at dose rates about 2 to 10 times higher for deciduoustrees. Prolonged exposures of only 0.5 mGy day-1 have been considered to result inincreased radiosensitivity due to unrepaired damage. Conifers are considered to die
as a result of dose rates of 120 to 240 mGy day-1 after a period of 2 to 3 years.
Cereal plants have also been the subjects of many studies, particularly with regard to
mutation rates over a very wide range of dose rates.
(72) Conclusions drawn with respect to the not inconsiderable data baseavailable on the chronic effects of radiation on animals and plants are therefore often
as much affected by the way the data are collated and analysed, as they are to inform
upon specific questions. Thus the data have often been summarised not only in
relation to different groupings of animals and plants, but also in terms of different
bandings of dose rates, which include many different types of effects in manydifferent species within a phylogenetic group. It is probable that such summaries
have sometimes been influenced by a belief that dose rate ‘guidelines’ have been
recommended by the IAEA. This is not the case. Various conclusions were drawn
by members of an IAEA panel, on the status of the available scientific information,
which was published in an IAEA Technical Reports Series (IAEA, 1992), but these
did not constitute official IAEA guidance. Dose rate limits for biota have not been
adopted in the IAEA Safety Standards; indeed, the IAEA has continued to develop
its approach to the subject considerably since then (Linsley, 2002; Robinson, 2002;
Gonzalez, 2003). More generally, however, such summaries of the existing data
have found it difficult to draw up a clear picture of the relationships between doseand effect for different types of animals and plants within the context of theirnormal, environmental, life histories.
(73) Reviewers have also, explicitly and understandably, usually omitted thelarge amount of data that have been derived from laboratory studies of mammals forthe purposes of improving the radiological protection of humans, particularly withregard to stochastic effects. As a consequence, none of this data base has been
examined with respect to the potential risk and consequences of stochastic risks forthe same species in the wild. Such an evaluation needs to be done, for it is the best
biologically understood radiation effect. All of these reviews also draw attention to
the very large and difficult-to-summarise data bases with regard to RBE in different
plants and animals.

6.

ISSUES RELATING TO THE USE OF DEFINITIONS, TERMS,QUANTITIES AND UNITS

6.1. Introduction(74) Existing practice and recent reviews display a broad range of terms,
definitions, and modifying factors with regard to discussions of both the estimation28

29
of radiation dose rates and the effects of radiation. With regard to the latter, because
the effects of ionising radiation are influenced by the dose, the dose rate, and thequality of the radiation, it has long been recognised that a set of unambiguous
definitions of the relevant basic quantities is essential in order to provide a soundsystem for the radiation protection of human beings. Several terms have been used
specifically for human radiation protection, and these are kept under constantreview. But for the protection of other species, only the quantities describing thebasic physical factors of radiation absorption exist, although various attempts andsuggestions have been made to provide greater flexibility, and to allow for the
known but limited information available in relation to radiation quality.
6.2. Recent concepts and terminologies with respect to animals and plants(75) In contrast to the situation with human radiation protection, there is atpresent no formal or universally accepted approach for making allowance of suchfactors as LET or RBE in the description of absorbed dose by any other animal, or
any plant, and hence of use in evaluations of environmental radiation protection. The
need for such an approach has been widely recognized, for several different reasons.
Firstly, it is known that the RBE phenomenon exists in animals other than man;indeed, much of the RBE information used in human radiation protection has been
gained from animal studies and thus it seems reasonable that allowance should bemade for it in the assessment of the relationship between dose and effects for thosesame animals. Secondly, it is known that many animals and plants have very highlevels of naturally occurring alpha-emitting nuclides in their tissues, and thus the useof weighting factors would be useful in attempting to normalise comparative
radiation background dose rates. And thirdly, many environmental protection
problems relate to concerns over the actual or potential presence of alpha-emitting
nuclides, and thus the fear that their potential effects on wildlife could beunderestimated if such RBE factors were not taken into account.
(76) Because of these difficulties, there have been various attempts in recent
years either to address them, or at least to highlight them. Thus UNSCEAR (1996)
suggested that a weighting factor of 5 be used for internal α-emitters, for all living
things other than man; this suggestion was made in the belief that deterministic
effects would be of the greatest significance.
(77) Subsequently, Pentreath (1999), in proposing the setting up of a set ofreference fauna and flora, considered that some method of expressing radiation
exposure in terms other than Gy was essential, both in order to describe backgrounddose rates adequately, and to estimate additional dose rates equitably amongst
different radionuclides. Two approaches were suggested. One was simply to refer tohigh and low LET components of the dose rate separately, which was considered to
be clumsy; the other was that something along the lines of an equivalent dose bederived, analogous to its use in radiological protection of humans, and that thismight be called the dose equivalent for fauna and flora (DEFF). The deliberate
inclusion of the phrase “dose equivalent” in this definition was intended to help
distinguish it from “equivalent dose” used in human radiological protection. The
DEFF was defined as the product of Gy and a ‘qualifying factor’ (qf). The starting
place for the latter was seen to be, as it had been for the rem, the hard factual
information relating to linear energy transfer of radiation in water. It was consideredthat this would provide values of 1 and 20 for beta/gamma and alpha radiations29

30
respectively, and could be used until more reliable or relevant information became
available with respect to particular types of effects in different types of organisms.
(78) Developing this approach further, it was also considered that the use of theDEFF term for specific types of fauna and flora (DEFFF) would need to be set out insuch a way that the relationships between any qualifying factor and absorbed dose
could accommodate a range of different values, not only in relation to the type ofradiation (particularly for alpha radiation) but also for the specific types of reference
organisms and effects upon them that might eventually be used in an international
system (Pentreath and Woodhead, 2001). As a general starting point, they
considered that some form of radiation weighting factor might be derived as thequotient of the accepted maximum and minimum values of the linear energy transfer
in water for α-particles, with energies up to 10 MeV, and the maximum andminimum LET values for electrons with energies in the range of 0.01 to 2 MeV. But
as this approach yielded values substantially larger than observed RBE ranges forlow dose rates of high-LET radiation, it was suggested that actual RBE values
relating to the chosen types of fauna and flora should be used to compile a set of(DEFFF) values. And, in order to be generally conservative in those cases where
there was no experimental data relevant to such types of fauna and flora, it wasthought that a provisional value of about 40 might be adopted, based on the verylarge range of data available in the existing literature, until the subject had been
examined in more detail.
(79) In the meantime, Trivedi and Gentner (2000) had suggested a somewhat
different approach: that of deriving a weighting factor in order to arrive at anequivalent dose for protection of non-human biota. Starting from the existing ICRP
approach to human radiation protection, they suggested the term ecodosimetry
weighting factor, (eR), for all non-human biota to fill a role equivalent to thatoccupied by wR in human radiation protection. Thus they considered that (eR) should
not reflect values for stochastic effects at low doses, because they considered that
not all non-human species develop cancer or receive doses that they considered low.
Furthermore, they considered that although the value for eR should take account ofvarious RBE values for effects from environmental levels of doses, it should not belimited to these inputs.
(80) In looking at the considerable range of α-emitter RBE values for endpoints
involving reproductive and haemopoietic systems, Trivedi and Gentner (2000)
concluded that, in a number of situations where very high RBE values had beenreported, uniform distribution of the radionuclides are typically assumed, which may
not reflect the ‘real’ dose to the critical target. They therefore proposed that RBE
values from experiments with fission neutrons, where dosimetry is not an issue,
might be used to guide selection of eR for α-emitters. They also evaluated reported
values for RBE for alpha-emitters and determined that the most “realistic” values
ranged between 2 and 12. This was interpreted to indicate that the suitable RBE
values for alpha-emitters in biota generally are between 5 and 10. Kocher andTrbalka (2002) also expressed the view that an appropriate value probably lies in therange of 5 to 10.
(81) Yet another suggestion came from an IAEA working group on “Quantities,
units and compliance” (IAEA, 2000). They suggested that the term (radiation)weighted absorbed dose (rate) be used generally for protection of the environment
to fulfil the purpose served by equivalent dose in the system of radiation protection30

31
for man. This group defined ‘wr’ as the “radiation weighting factor appropriate tothe organism, effects endpoint and dose rate”.
(82) And at about the same time, Environment Canada (2000) had proposed aradiation weighting factor for assessing the effects of alpha emitters generally in theenvironment under Canada’s Priority Substances List 2 (PSL2) based on a paper byThompson et al. (2003). While acknowledging that the majority of studies reported
RBE values <10, these authors selected studies that they deemed to have“ecologically significant endpoints and at environmentally relevant doses and dose
rates”. The geometric mean RBE from the selected subset was 40. Their value wasdescribed as a recommended RBE weighting factor for the ecological assessment of
ecologically significant alpha-emitting radionuclides.
(83) The CNSC’s Advisory Committee on Radiological Protection subsequently
provided a detailed critique of the recent studies that have yielded RBE values foralpha radiation significantly greater than 20 (ACRP, 2002) and recommended that aradiation weighting factor in the range of 5 to 20 for alpha particles, relative to lowLET radiations, would be appropriate for protecting all biota against ‘ecologically
relevant deleterious effects’. The ACRP also concluded that studies that imply
higher RBE’s for some endpoints in animals all have serious problems, either with α
dosimetry or with poor statistics. Chambers (2003) has also commented on themethodological flaws in the studies that purport to support high values of RBE foralpha emitters.
(84) This debate over what values may or may not apply in different
circumstances will no doubt continue. What is clear, however, is that the issue of thedevelopment of one or more factors to modify the quantity of absorbed dose inanimals and plants needs to be addressed, and addressed logically. The issue,
therefore, is not simply about the numerical derivation of a particular value, but
about the concepts and assumptions relating to the need and function of one or morequalifying or weighting factors. Until these issues are resolved, there is no basis
upon which any common numerical value can be based.
(85) The principal areas that need to be considered appear to include the needfor some basic assumptions with regard to the importance of LET with respect to all
forms of biological tissues; the need to allow for the fact that the RBE response canbe demonstrated in a wide range of biota; the relevance of the biological endpoints
used in RBE studies with respect to the many different objectives of environmental
management and protection, and in particular to the categories of effects relating toReference Animals and Plants; the extent of data available on RBEs relating to eachone of the ICRP set of Reference Animals and Plants; and the extent to which it ispossible to generalise or extrapolate amongst these data (e.g., amongst mammals ingeneral, or vertebrates, or invertebrates, or plants). This report cannot address all ofthese issues, but a key one is clearly that relating to the concept of RBE. This subject
has recently been the subject of an exhaustive review in the context of humanradiation protection (ICRP, 2003b) but the following points need to be noted here.
(86) The radiation weighting factors for protection of human beings areprimarily based on the need to reduce the risk of stochastic effects, and therefore
have a pronounced emphasis on the response to radiation at low doses. In otherwords, the RBE values used to guide decisions on radiation weighting factors are thelow-dose maximum RBE (RBEM) values. There are two approaches to the3132
determination of RBEM (ICRP, 2003b). A low dose method, that determines RBEM
as the quotient of the initial slopes of the reference and test radiations; and a highdose method, which has been applied to determining RBEM for neutrons, that
divides this value by the dose and dose-rate effectiveness factor (DDREF) selected
for use with human low-LET acute exposure risk coefficients. The high dose method
therefore implicitly argues that low dose-derived RBE values for stochastic effects
in humans should be divided by a factor of at least two when applied to high doses.
(87) Factors that are known to effect the determination of RBE values include
the effect of selected dose range; the effect of dose rate; the effect of endpoint
selected for assessment; the effect of errors in dosimetry; and the effect of choice ofthe reference radiation. Indeed, there is probably no such readily identifiable entity
as the RBE for a particular type of radiation that can be generally applied. Instead,
there are a number of RBE values, which differ appreciably. It should also be notedthat the RBE is only one type of input to the selection of radiation weighting factors,
and the limitations of the concept must be borne in mind, particularly with regard toconsideration of the levels of effect assessed and the dose range within which theselected levels of effect occur.
(88) Chambers et al (2004) have identified 66 relevant measurements of alphaRBE, and assigned these to one of three broad categories: population relevant
deterministic endpoints such as cell mortality, oocyte mortality and sperm mortality;
other deterministic endpoints such as haemopoiesis, spermhead abnormality and lens
opacity; and stochastic endpoints such as chromosomal aberration, double-strand
breaks and mutation.
(89) Another issue is that of making allowance for the non-homogeneous
distribution of internal nuclides. At a practical level, this will to some extent dependon the size of the organisms and the dosimetric models that are applied to them. It
will also depend upon the type of biological effect observed and its relationship todose. As yet, it is impossible to draw any conclusions, except that it is an issue that
may need to be addressed for some types of animals and plants.
6.3. Discussion(90) The system for radiation protection of human beings is based on dose, andupper boundaries on what constitute acceptable degrees of risk from radiationinduced stochastic effects are provided by the system of dose limitation. Exposures
are generally received as a series of highly fractionated, acute, but low doses. And
although the dose limit is specified on a per annum basis, it is assumed that,whatever the dose rate, the exposure should have an effect no greater than if
delivered in a protracted (i.e. chronic exposure) manner (UNSCEAR 2000).
(91) Radiation quality factors have been derived for the application of dose
assessments for humans, for which stochastic effects are primarily important.
However, it is not clear to what extent such effects are of relevance with respect toanimals and plants, and even if they were, their significance would probably beconsidered under different categories of biological endpoints of interest. The
absorbed dose therefore remains the key quantity for exposure assessment of biota,
although this could usefully be further evaluated in terms of high and low LET.
3233(92) Looking to the future, the assessment of probability of causation (forexposed persons who have developed cancer) may be a more informative modelwith respect to how an RBE might be used in the protection of non-human biota.
Such values are computed for intermediate or high-dose exposures that cause risksof a magnitude comparable to the background risk (ICRP 2003b). Thus neither thevalues of RBEM nor the weighting factor conventions wR and Q(L) are applicable;
instead, other dose information needs to be applied. Such considerations may be
germane to non-human biota.
(93) For the purpose of pollution control, the above protection objectives may
require the explicit demonstration of the avoidance or minimisation of harm to theenvironment, or the ability to deal with an environment that is already deemed tohave been harmed. And, for the purpose of nature conservation, the above protection
objectives may, in turn, require assessments to be made of the likelihood of harm toindividuals of particular species, or to potential or actual effects on populations of
one or more species, or to the sustainability of the ecosystem
7.

ASSESSING EFFECTS IN TERMS OF DERIVED CONSIDERATIONLEVELS7.1. Introduction(94) In the meantime, however, some form of practical means is required inorder to make judgements based on our current knowledge of the effects of radiation
on different types of animals and plants. Thus although there is a reasonable amountof information relating to various types of radiation effects, these are almost entirely
with respect to relatively high dose rates and total doses. And because such effects
are primarily of a non-stochastic nature (with the exception of data derived fromsmall mammalian studies) it is difficult, in the absence of any form of ‘sliding scale’
against which to apply some form of ‘risk related’ criteria, to make assessments or
judgements at lower dose rates. A different approach is therefore required.
7.2. Derived Consideration Levels(95) It has therefore been suggested that the only other useful comparator might
be that of the natural background radiation dose rate normally experienced by suchanimals and plants (Pentreath, 1999, 2002a). Additional doses that were but
fractions, or small multiples, of the normal background dose rates might therefore be
unlikely to be the cause of any environmental managerial concern, particularly when
considered against those multiples of background dose rates that were known tohave specific effects. Dose rates that were very much higher, and in the region of
known or expected effects, would however need to be considered further, alongsideother environmental information, within any particular environmental management
framework. Thus, collectively, all of the derived information relevant to each type ofanimal and plant could be simplified into multiples of their background radiationdose rates in the form of Derived Consideration Levels. Such data could then beconsidered alongside other information (such as the size of the area affected, thefraction of a population exposed, and the actual animals and plants concerned) in33

34
order to satisfy the legal framework within which any management action was being
taken.
(96) A useful first step, therefore, would be the compilation of data with regard
to both the natural radiation background dose rates, and what is known about
specific categories of radiation effects for the Reference Animals and Plants. With
respect to the former, the following information is of relevance. In the aquatic
environment, dose rates are expected to be about 1 to 10 μGy day-1 for adult benthic
fish (IAEA, 1976; Copplestone et al, 2001; Brown et al, 2004); within a range of 2
to 14 μGy day–1 for adult benthic crustaceans (crab) and molluscs (marine snail)(IAEA, 1976; Brown et al, 2004); and about 2 to 12 μGy day–1 for macrophytes(seaweeds), based on northern latitude data (Brown et al, 2003). Broadly similarvalues have also recently been calculated for European waters generally (Brown etal 2004), but for a different set of natural radionuclides, and for less precisely
defined biota. For the freshwater environment, pelagic fish are considered to havebackground dose rates of about 0.5 to 18 μGy day–1 (Brown et al 2004).
(97) With regard to the terrestrial environment, external dose rates of about 2
μGy day-1 have been calculated for earthworms within the soil, and 0.6 μGy day-1
and 0.8 μGy day-1 for deer and mice respectively on the soil (Gomez-Ros et al,2004). Internal dose rates vary very considerably from one organ to another, andfrom one type of animal to another, making it difficult to draw any clear picture of
total average body dose rates. Nevertheless it has been estimated that dose rates
from 210Po in some tissues in some mammals could be in the range of 40 to 80 μGy
day-1 and as high as 0.2 to 7 mGy day-1 to the lungs of small mammals living in thesoil from radon (Gomez-Ros et al, 2004). Terrestrial plants have a total dose rate ofabout 2 to 20 μGy day-1 (Copplestone et al, 2001).
(98) Secondly, it is necessary to compile data sets of what is known about theeffects of radiation, across a range of dose rates, with respect to different types of
biological damage. For some of the Reference Animals and Plants, relatively gooddata sets exist. There are large data bases relating to rodents, across a reasonable
spectrum of dose rates, but such data need to be evaluated carefully because of theselection of certain strains of rodents in experiments designed to obtain data of a
specific nature, particularly with regard to carcinogenesis, for human radiologicalprotection. There are also various data sets covering several orders of magnitude ofdose rates for several types of fish. And, for the Reference Pine (as summarised by
Copplestone et al, 2001; Real et al, 2004) it is known that dose rates in the range ofabout 2 to 25 mGy day-1 can have effects such as reduced trunk growth in mature
trees, and morphological alterations in pine needles. Such dose rates can eventuallylead to mortality in some trees. Decreased stem growth in saplings, and reduced
photosynthetic capacity, and thus reduced growth, has been observed at dose rates in
the range of 24 to 120 mGy day-1, and reduced seed production and germination atdose rates of 240 to 480 mGy day-1. For other fauna and flora, however, the databases are largely confined to effects observed at these very high dose rates and overrelatively short periods of time. Nevertheless, various data are available on all of thetypes of Reference Animals and Plants selected.
(99) The question naturally arises as to whether or not it is reasonable, or useful,to try and draw generalisations from the existing data. At this stage, the mostsensible approach would appear to be that of keeping the data sets separate, for each
Reference Animal and Plant, for the following reasons. Firstly, it is clearly unsafe to
generalise without considering individually the quality and quantity of the data34

35
across these different types of animals and plants. Secondly, there is as yet no
general theoretical basis for doing so, and the experimental information is extremely
varied. Thirdly, it is not clear as to what level of taxonomic division it would makesense to attempt to do so. And fourthly, the basic purpose of the Reference Animal
and Plant approach is to assemble information that can be used for different
environmental management purposes. These may specifically relate to one particularanimal or plant type (such as large terrestrial mammals, or waterfowl) or to mixturesof types relevant to particular habitat types (such as wetlands, estuaries, or forests)
for which particular combinations of animal and plant data would be required. All ofwhich, naturally, leads to further consideration of how such information on a limited
set of fauna and flora might be used.
7.3. Creating a Reference Set
The ICRP set of Reference Animals and Plants will therefore initially consist of an
extended biological description for each of the twelve types, plus the following data
sets for each type:(a) the dimensions of each primary or secondary model used to represent eachtype at one or more stages of its life cycle (as, for example, in Table 3);(b) a set of ‘dose per unit concentration’ values (μGy day-1 per Bq kg-1) forinternal and external exposures, for all of the principal naturally-occurring
radionuclides;(c) a set of ‘dose per unit concentration’ values (μGy day-1 per Bq kg-1) forinternal and external exposures, for all of the principal artificially-occurring
radionuclides;(d) a set of ‘reference’ internal naturally-occurring radionuclide concentrations(Bq kg-1);(e) a set of ‘reference’ external naturally-occurring radionuclides (Bq kg-1) forseawater, fresh water, and soil;(f) a set of ‘reference’ background dose rates (μGy day-1) for each type, using
the data in (a),(b),(d) and (e) to create the baseline of the Derived
Consideration Levels (DCLs);(g) a set of guideline ‘transfer factors’ and ‘concentration factors’ for the set ofartificial radionuclides;(h) and a set of information, set out logarithmically, summarising what iscurrently known about the effects of radiation on that type of animal or plant(these are the bands within the DCLs).
7.4. Potential applications(100) The need to make evaluations of the impact of radiation on theenvironment, either now or in the future, may arise for reasons that stem from any or
all of the various environmental management requirements discussed in Section 3.2,
but particularly in relation to pollution control and nature conservation, or under thegeneral guise of what might be termed an environmental impact assessment.
(101) Such needs may also include any of a number of objectives, each of whichmight need to be expressed, and deemed ‘acceptable’ or otherwise, in different
ways. These might include assurance of the public or their politicians, at national orinternational level, of the likely environmental impact of any actual or proposed35

36
practices, and demonstration of the ability to deal with any consequences in theevent of accidents or emergencies. They might also relate to compliance with thespirit or the letter of trans-national general pollution or wildlife-protection
obligations; to compliance with national pollution control licensing requirements forparticular industrial practices, sites or areas; or to compliance with the requirementsof specific national wildlife and habitat protection legislation.
(102) For the purpose of pollution control, the above protection objectives may
require the explicit demonstration of the avoidance or minimisation of harm to theenvironment, or the ability to deal with the environment that is already deemed tohave been harmed. And, for the purpose of nature conservation, the above protection
objectives may, in turn, require assessments to be made of the likelihood of harm toindividuals of particular species, or to potential or actual effects on populations of
one or more species.
(103) In order to make an evaluation of the effects of radiation on theenvironment itself with respect to any particular situation or practice, there areclearly several factors to consider, including the radionuclides of interest, theirsources, their previous inventories, their rates of introduction, and theirenvironmental distribution and fate. This basic information is also required in orderto protect the general public. Many numerical models therefore already exist that canbe applied to different practices, situations, and ecosystems. However, forenvironmental protection, other information is necessary, such as the potential
exposure to radiation of the fauna and flora within the area of radionuclide
distribution; plus the likely consequences for them, in terms of radiation effects. Of
these two, addressing the former should not be too difficult, the nature of the
problem having much in common with the environmental information needed forhuman radiation protection. The latter, however, is more difficult, and the term
‘consequences’ is far more open-ended than it is for human protection; many otherfactors therefore need to be considered, not least the original objectives of theassessment.
(104) Common to all of the protection objectives, however, is the process of
having to assess the situation and then, if necessary, consider the various options for
managing whatever situations may arise. This is particularly important whenattempting to understand the purpose of the environmental evaluation, because eachcomponent may need to make use of completely different approaches andinterpretations. But what should be common to both assessment and management isthe basic scientific understanding, plus the means of expressing and using therelevant scientific information. This has been the basis of success for theradiological protection of humans, and therefore needs to be carefully consideredwith respect to protection of the environment generally.
(105) In order to make an evaluation of the effects of radiation on theenvironment itself with respect to any particular situation or practice, there areclearly several factors to consider, including the radionuclides of interest, theirsources, their rates of introduction, and their environmental distribution and fate.
This basic information is also required in order to protect the general public. Many
numerical models therefore already exist that can be applied to different practices,
situations, and ecosystems. However, for environmental protection, otherinformation is necessary, such as the potential exposure to radiation of the fauna andflora within the area of radionuclide distribution; plus the likely consequences forthem, in terms of radiation effects. Of these two, addressing the former should not36

37
be too difficult, the nature of the problem having much in common with theenvironmental information needed for human radiation protection. The latter,
however, is more difficult, and the term ‘consequences’ is far more open-ended than
it is for human protection; many other factors therefore need to be considered, notleast the original objectives of the assessment.
(106) It also has to be recognised that, in many cases, much more specific data on
local animals and plants may already be available with respect to specific sites; orthat data are often required for organisms that are more relevant in other respects,
such as their ecological importance at a local level. But the data sets will always belimited because of the sheer impracticality of ever deriving some of the required
information – such as that relating to radiation effects. Such organisms might
therefore be regarded as secondary reference animals and plants, provided that they
could be shown to relate in some way (for example by using the same sort of
dosimetry models) to one or more of the ICRP set of Reference Animals and Plants.
There are, therefore, a number of issues relating to our ability to extrapolate fromlimited data bases and frameworks in order to deliver environmental protection in a
wider and practical sense.
(107) It is not currently possible to provide recommendations as to how to
perform extrapolations that have general applicability, and thus each case has to becarefully considered on its own merits. Due to the relative paucity of information,
the main cases for extrapolations, and challenges for methodological development,
include the following. There are clearly issues with regard to extrapolating fromhigh acute doses and dose rates (several Gy at about10 to 100 Gy h-1) of low LET γand X-rays to lower doses accumulated at lower dose rates (about 1 to 100 μGy h-1).
In the radiobiological and radioecological literature, the qualifiers “low-level”,“chronic”, “higher”, “acute” and so on are often used without any definition. But aradiation exposure lasting several days may be effectively “chronic” for a short-lived
organism, and yet effectively “acute” for a long-lived organism. Unfortunately, there
are very few data that relate directly to the chronic, low-level irradiation conditionsof relevance for animals and plants in the wild i.e. exposures at dose rates of 100 1000 μGy day-1 over the life span of the organisms, and the response endpoints mostcommonly assessed after acute, high dose, irradiation are not those that are relevantin such situations.
(108) Another issue is that of extrapolation from one organism to another.
Although the information is limited, there is clear evidence that there are substantial
variations in the radiosensitivity of organisms, both within and between taxonomic
groups. This differential sensitivity also extends to different stages of the life cycle
for any given organism. Extrapolation should become easier the more closely relatedorganisms are, and the more similar the effects’ endpoints considered for the
relevant stage in the life cycle (Strand et al, 2003; Garnier–Laplace et al., 2004).
(109) And finally there is the issue of extrapolation from effects in the individualorganism to possible impacts at the population and community levels. This will also,
in many cases, involve the extrapolation from laboratory conditions (where mostexperimental information originates) to field conditions (where populations interact
with the physical environment as well as with other organisms). Interactions at
community and ecosystem level can be particularly complex (Brechignac, 2003;
Doi, 2004; Hinton and Brechignac, 2004). Nevertheless, it is necessary to start37

38
somewhere, and by developing an understanding of the effects of radiation on alimited number of animals and plants, at the individual level, and exploring both theconsequences of such effects at their population levels, and amongst different
populations, a broader understanding will develop against which these wider issues
can be assessed.
(110) The use of the above set will therefore clearly depend upon the ‘questions’that are asked, but these may be, just as an example, along some of the following
lines. In a comparative, theoretical, exercise the environmental distribution ofradionuclides in one or more environmental situations (e.g., seawater) would beapplied using the data sets for the relevant Reference Animals and Plants in order tocalculate the expected ‘additional’ dose rates. The results could then be comparedwith the relevant data sets in the bands of Derived Consideration Levels to consider
what management action would or would not be warranted. Dose rates that werefractions or small multiples of the background values would be unlikely to be ofconcern; dose rates that were in the range known to cause particular effects inindividuals of that type of animal or plant would prompt further consideration, suchas the area over which such dose rates were likely to obtain, for how long, whatfraction of the local population might be exposed, and so on, depending on what
information was being sought, by whom, and why.
(111) In a ‘normal’ situation, one might first of all wish to calculate the actual
external or internal background dose rates for one or more of the selected types ofReference Animals and Plants by making use of locally derived radionuclide
information, but using the same modelling approach. Thus the relevant data sets
would be used to make such calculations. The extent to which the calculated
background dose rate differed from the ICRP reference set would be noted. Then theactual ‘additional’ dose rate from the practice could be calculated, again using thedata sets, and a judgement or evaluation made, as in the first example.
(112) Where, again in for example a ‘normal’ situation, animals or plants very
close to any of the twelve types of Reference Animal or Plant do not exist, or are not
the features of interest, then locally derived information might need to be derived forany of the purposes set out above, but particularly with regard to calculating the‘additional’ dose. But comparisons could still be drawn with the ICRP reference set(as is the case for calculating human exposures where necessary) and it is likely thatthe data sets used in the Derived Consideration Levels would still be of value inassessing the likely effects and consequences, if any. And in all such cases, it isexpected that other types of assessments, using non-Reference Animal and Plant
types, will still find it useful to use the ICRP set to draw comparisons. Thus othertypes of organisms may be considered to be similar to one or more of them, or lying
somewhere in between two or more types of Reference Animal or Plant. In all cases,
however, the basis for the calculations and decisions will be transparent andauditable, and amenable to amendment and expansions as further or improved
scientific information becomes available.
(113) The consequences of any expected radiation effects may need to beevaluated with respect to individual animals and plants, depending on the legal
framework within which action is being considered, but undoubtedly the major
requirement will often be the need to make evaluations at the population or
ecosystem level. Radiation effects on higher levels of biological organisation (e.g.,
populations and ecosystems) occur only if individual organisms are affected, andradiation effects’ data have generally been obtained for individuals rather than for38

39
higher levels of organisation. In the natural environment the situation can become
very complex because of the interactions between each individual and its
surrounding ecosystem. The effects can also be modified by the presence of otherenvironmental stressors, or by combined effects related to the presence of otherpollutants, and by interactions between different trophic levels. Because radiation
effects at the population level – or higher – are mediated via effects on individuals ofthat population, it therefore seems appropriate to focus on radiation effects on theindividual for the purpose of developing a framework of radiological assessmentthat can be generally applied to environmental issues. This approach is consistent
with many of the existing assessment methods for non-radiological environmental
contaminants. It is also essential in order to consider how effects such as reduced
reproductive success can be interpreted in the context of the normal biology ofdifferent types of plants and animals. Even the concept of what constitutes a‘population’ will differ amongst the various ‘types’ of Reference Animals andPlants.
8.

SUMMARY AND CONCLUSIONS(114) The criteria for selecting a small set of Reference Animals and Plants stemfrom the operational needs of different approaches to environmental protection, as
required under different legislative and environmental management regimes, plus
the reality of our current limited amount of relevant data, and the prospect ofimproving upon such a data base in the near future. Nevertheless, it is possible toselect about a dozen types of animals and plants that are typical of the major
environmental sectors of interest, for which there is a sufficient amount of data
available to at least begin the process, and to develop it to a useful and operational
stage fairly quickly.
(115) There are certainly sufficient approaches to modelling dose rates at thewhole body level, although certain further refinements are required, particularly forthe larger animals and plants. More problematic is the lack of a clear means ofexpressing dose rates across different bands of LET radiation, and across all of thedifferent phylogenetic groups. The data relevant to different categories of biologicaleffects is also somewhat limited, but greater use could be made of the data that doexist.
(116) Collectively, therefore, it has been possible to select, define, and describein outline a number of Reference Animals and Plants that could be used by the
ICRP. With regard to the availability of dose models, a number of suitablemodelling approaches already exist, but these would still need to be tailored to thespecific types of Reference Animals and Plants selected. Various issues relating to
the dosimetric quantities and units that could be used for such organisms have been
discussed, and it is evident that doses to biota can only safely be described at present
in terms of Gy, although this could be expressed in terms of high and low LET
components. A clear priority for the future is to examine further how best to relatedose, and internal distribution of dose for the larger organisms, to the relevant
radiation effects across different forms of animals and plants. In parallel, however, it
will also be necessary to examine the extent to which the large data base on
mammals with respect to stochastic processes and effects (which has been derived
largely under laboratory conditions to aid human radiation protection), can beapplied to the same and other types of mammals in the wild, and its relevance to thesame categories of effects. The large data base on RBE values also needs to be more39

40
rigorously evaluated to see to what extent, if at all, generalisations can be madeacross different phyla, and between animals and plants.
(117) The end-points for assessing radiation effects in non-human species of
relevance to environmental management practices would appear to be those which
can be categorised as early mortality; morbidity (particularly with regard to plants);
reduced reproductive success; and various forms of cytogenetic damage. Bands ofdose rates, relative to the natural background dose rates of different types of animals
and plants (Derived Consideration Levels) could then be compiled in order to aid
environmental management decision making, although the availability of relevant
data is currently very varied, and is of differing accuracy and precision. But,
nevertheless, there are sufficient data to begin the process of developing system forassessing the protection of non-human species and guidance for management
decisions concerning protection of the environment that is based on the same
principles, and uses the same basic scientific understanding, as the approach used forthe protection of human beings.

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